A retractile grab device, suitable for extracting and recovering submerged concrete blocks which form part of the protective structure at harbours and marine docks. The device of the present invention operates with a crane or similar mechanical driving means that supports it and from which the operating tasks are performed, and is capable of executing a prehensile movement between its claw elements, whereby it takes firm hold of a submerged block and raises and deposits it any chosen place.
The construction of protective dikes and counterdikes at harbours and marine docks has always been done on a permanent basis in view of the enormous effort and high costs involved in removing the thousands of large-sized rocks or concrete blocks that usually make up facilities of this type. Nevertheless, either because of the strategic location of the harbour, the existing network of logistic infrastructure in the area, the proximity of a series of industrial plants that make use of it, the lack of a suitable nearby place for the construction of a new port, or for any other reasons, when the decision is made to enlarge a port, it usually becomes necessary to withdraw a part or all of those immense and diverse structures forming the protective dike. In this removal operation, as a rule, it is necessary to extract the loose materials forming the core of the structure, as well as the large rocks or concrete blocks which, with their prismatic or similar constitution, usually form the layer protecting and sheltering the structure from the action of the sea and which make up its rockfill.
The procedures used nowadays for the partial removal of blocks which have normally been randomly put in place are arduous, entailing manual labour, a high risk for the operators doing the job, and an extremely high cost, due to the fact that thousands of blocks typically need to be moved.
One of the procedures used for operations of this type consists of one or more operators submerging and placing a grappling chain or a polyester sling around a block so that it may then be lifted. This procedure is then repeated for each block.
Another method used in these operations is to drill holes in the blocks, also done by submerged operators, and then secure rods in them with resin so that they may be grasped and lifted.
But as it will be readily appreciated, these substantially manual procedures are extremely costly, as in the best of cases the outputs obtained per working day do not exceed the withdrawal of between five and fifteen blocks. In most cases, then, the work requires an inordinate amount of time, which generally results in completion of only partial removal operations being carried out.
In view of the foregoing, as well as many other drawbacks well known in the art, the present invention has been devised.
One purpose of the invention is to provide a suitable device for the recovery of the blocks forming this sheltering structure, which device is capable of acting individually on the blocks to be removed and of lifting them out irrespective of the position they are in. The device of the present invention can perform this task without having to determine the specific location and placement of the blocks beforehand, and carries it out by mere trial and error in an extraordinarily short time compared with the times spent on the procedures used currently and with a success rate in this trial and error process that is close to one hundred percent.
Another important aim hereof is to provide a device, wherein the work of extracting the blocks does not involve manual labour at all, except for the operator controlling the crane supporting the device. This is the same person who controls the inventive device, so there is no risk of injury during the block extraction process.
A further aim of the device is to provide a device as described, in which all the constituent parts are purely mechanical, conferring upon it a strength in keeping with the aggressive environment in which its work will be performed, being moreover suitable to adapt itself perfectly and to work with the vast majority of tractor means used for this type of work.
Yet another object, equally important for the impact on the surrounding environment, is that the device is designed to recover the blocks without impairing their basic characteristics, so that they may be put to use again in any new structure. This is significant not only because of the recovery of the materials involvedxe2x80x94a savings which it may be readily appreciated is substantialxe2x80x94but because it avoids a wide range of environmental problems which are entailed in concrete making processes, as experts on the matter are fully aware.
Another object of the invention is to provide a simple and versatile device in which its general structural principles facilitate a practical embodiment for use with blocks of widely varying weight and mass, as it is possible to build a device suitable for handling cubic, prismatic or any amorphous-shaped blocks from one metric ton or less up to a device able to move blocks of ninety or one hundred tons of similar shape, which is the range that comprises most of the blocks used in structures of this type, as well as for blocks of any intermediate size, all on the basis of the aforesaid general structural principles defining the invention.